PLANT DISTRIBUTION AND ASSOCIATIONS. XXV11. 



Having now sketched the external relationships of the 

 plants of the parish, it remains to consider their internal dis- 

 tribution and to distinguish the plant societies 

 Lowland which are most characteristic of the district. 



Division. It has already been stated that altitude is the 



most important factor in the problem, and the 

 500 feet contour line, perhaps, makes the most natural division 

 between the lowland area in the east of the parish and the 

 much more extensive upland area. Though it is not conveni- 

 ent to adhere closely to this division, its existence cannot fail 

 to strike anyone who is familar with the flora of the parish. 

 The lowland division can claim three plant societies, which, as 

 such are entirely absent in the higher area, though a few of the 

 individuals may rise above 500 feet. These are the still- water 

 aquatic plants : the colonists, denizens and casuals of arable 

 and waste ground, which include most of the species of annual 

 duration only ; and a group of woodland and hedgerow plants, 

 viz. : Ranunculus auricomus, Sisymbrium A Maria, Acer campestre, 

 Rosa arvensis, Galium Cruciata, Convolvulus sepium, Solarium Dulc- 

 amara, Linaria vulgaris, Siachys Betonica, Lamium Galeobdolon, 

 Tamus communis, Arum maculatum and Carex pendula. The plant 

 associations of the woods and cloughs are so interwoven, that 

 it will be better to put them by themselves, especially so, as 

 they form the transition from the lowlands to the uplands, and 

 appertain to both, and lead us naturally to the flora of the hill- 

 side pasture, and to the various types of moorland. 



The mill-dams and the canal (including Tag Lock and the 

 Old Cut at Norland) are the only stagnant, or slowly-moving 



waters in the parish, in which all the principal 

 Aquatic adaptations of hydrophytic plants to their 



Plants. aquatic environment may be observed. Using 



the word ' pond ' for these areas as it suggests 

 the exact conditions that prevail, the pond vegetation forms a 

 number of communities, distributed in irregular zones in ref- 

 erence to the bank. Proceeding from the deeper water to the 

 edge we meet in turn : 



A. — Free Floating Plants. In addition to the Algae and 

 Desmids, which are excluded from our enquiry, the only 

 phanerogam that maintains itself without any attachment to 

 the soil, and is a prominent feature in the " pond," is the duck- 

 weed, Lemna minor ; but L. trisulca and Ceratophyllum demersum 

 occur in the canal at Salterhebble. 



